Recurrent aphthous ulcers is a disease state of unknown etiology, characterized by painful, recurrent, single or multiple ulcerations of the oral mucosa. Localized trauma has been implicated as causative agent. The purpose of the study is to ascertain if injury to tissue has a role in initiating ulcers in patients known to have recurrent aphthous oral ulcers, as compared to a matched control population. Other lesions of the oral cavity also are being investigated. BIBLIOGRAPHIC REFERENCE: Archard, H.O., Denys, F.R., and Martinez, M.G.: Electron microscope observations of "keratin pools" in chronic hyperplastic oral mucosa. J. Oral Path. (1976) 5:371-384.